1. Field of the Invention
The present invention generally relates to a magnetic storage system, and more particularly to a spindle motor assembly.
2. Description of Prior Art
Magnetic storage systems such as hard disk drives, are information storage devices that store data on at least one rotatable magnetic disk. In conventional hard disk drives, a spindle motor is used to drive the rotation of the disk(s). The high-speed rotation (for example, 5400 rpm) of the disk(s) is achieved by fixing a hub, which integrally holds the disk(s), to the spindle motor and by transmitting rotation of the spindle motor to the hub. Information is written on or read from a disk by a head or magnetic transducer which is typically maintained at a predetermined distance above the surface of the disk (also referred to as "fly height"). The head is positioned over a desired track to read from or write to the desired track. If rotation of the disk is not accurately executed, then it becomes difficult for the head to follow the track, often leading to erroneous data when data is written to or read from the disk. Accordingly, the ability of a hard disk drive to maintain regular high-speed rotation without rotational distortion of the disk surface improves the overall performance of the hard disk drive.
As the demand for hard disk drives having larger storage capacity with reduced height dimensions increases, it becomes necessary to design a spindle motor with improved shock resistance. Hard disk drives typically mount the disk(s) on a hub which is mounted on the rotating member of the spindle motor. The manner in which the hub is mounted to the spindle motor may improve the shock resistance of the spindle motor. The mounting of the hub onto the spindle motor may be simplified by providing a bearing cartridge. A bearing cartridge typically refers to an assembly that includes a shaft, bearing balls, and a sleeve integrated and housed within a single cartridge.
A conventional bearing cartridge 20 is shown in FIG. 1. The bearing cartridge 20 includes a shaft 13, a sleeve 11, a plurality of bearing balls 12, and a retainer 10 for holding the bearing balls 12 on the circumference thereof at regular intervals. Grooves formed on the outer peripheral surface of shaft 13 and the inner peripheral surface of sleeve 11 determine the fixed positions of the bearing balls 12. The bearing balls 12 are retained in the grooves.
Referring now to FIG. 2, bearing cartridge 20 is assembled together with a hub 14 and a motor which includes a stator 17 and a magnet 15 to form a conventional spindle motor assembly. The magnet 15 is fixed to the hub 14. Shaft 13 includes a hub mounting portion 21 formed in the upper portion of shaft 13 to which hub 14 is attached. A flange 16 is attached to stator 17 which is positioned between sleeve 11 and magnet 15. By attaching hub 14 with shaft 13 in this manner, hub 14 is capable of rotating. The central hole of disk(s) can be inserted onto the outer periphery of the hub 14, such that the disk(s) may be attached to hub 14 by axially loading the disk stack with a disk clamping device such as a belleville spring type clamp with a fastener into shaft 13.
Bearing cartridges, such as bearing cartridge 20 shown in FIG. 1, are often used to simplify the hub mounting operation. Unfortunately, when conventional bearing cartridge 20 is mounted on hub mounting portion 21 located at the upper portion of shaft 13, the hard disk drive requires an increased height dimension. The increased height dimension is caused by the additional height added by hub mounting portion 21. Unfortunately, a reduction in height of hub mounting portion 21 to decrease the overall height of the hard disk drive often leads to an unstable attachment between shaft 13 and hub 14 which adversely affects the stable rotation of the disk(s).
Because a predetermined height is required to achieve a stable attachment between hub 14 and shaft 13, one approach is to narrow the pitch between the upper and lower bearing balls 12 within bearing cartridge 20. However, when the pitch between bearing balls 12 is narrowed in this manner, the shock resistance capability of the hard disk drive to external disturbances such as shock is reduced, thereby decreasing the likelihood that stable rotation of the disk will be achieved.